This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Currently, an electric vehicle (EV) typically comprises a battery bank and battery charging system. The battery bank typically requires direct current (DC) input to charge the batteries. To that end, an onboard charging circuit is provided that converts AC power typically found in the home to a DC input for the battery bank. In what is typically known as “level 1” and “level 2” charging, the battery charging system is provided with household or similar alternating current power, which it converts to DC in order to feed the battery bank. Level 1 and level 2 charging mainly differ by the amount of power supplied and sometimes by the voltage as well.
“Level 3” charging generally refers to DC charging, which can involve DC current at high power, e.g., voltages above 350V and high currents leading to charging powers that are typically above 15 kW and run up to 160 kW. Level 3 charging stations are commercial charging stations that seek to charge EVs as quickly as possible. With current EV batteries, very rapid charging can be achieved up to about 75% to 80% of the battery's charge capacity. With some EV batteries, charging from 15% to 80% of battery capacity can be done within 15 to 20 minutes of high power charging. After this point, charging is very slow, for example, it can take a number of hours to raise the charge level from 80% to 99%. Normally the customer will be encouraged to leave the charging station so that other customers can charge their vehicles. Such rapid charging is convenient for commercial charging station operations; however, it can shorten the lifespan of some EV batteries to be subjected to such high power charging. For example, it might be preferable in terms of battery lifespan to allow for 2 hours to charge a battery from 15% to 80% of capacity instead of 20 minutes.
The DC power for such charging is supplied from three-phase power mains that are normally made available to commercial installations and not residences. Three-phase AC electrical power can be efficiently converted to DC. Typically, this kind of charging is unavailable in residences where available power is also typically limited to below 60 kW. In certain places, for example, power supply to the residential panel may be capped at 200 A at 240V (RMS), giving a total available power, for all household use, of 48 kW. By providing such a power limit using a main circuit breaker, the local distribution transformer, which is often sized using “oversubscription” assumptions, is statistically protected against overload as a result of too many residences drawing too much power. Moreover, level 3 charging, when starting from an AC current source requires a rectifier circuit, which is typically not provided in the home because of cost issues among other reasons.
Current residential car charging systems behave essentially like a high-power appliance, drawing from, e.g., a clothes dryer pug. In level 2 charging, the power is typically limited to about 7 kW or less that is a load comparable to a clothes dryer (30 amps at 240 V is 7.2 kW). The charging unit installed in the home connects the main AC power to the vehicle through a breaker circuit so that the vehicle's on-board AC to DC conversion circuitry can charge the vehicle battery.
Most electric vehicles allow for “fast” DC charging in which case the AC to DC converter is external to the EV. An advantage of DC charging is not only that the charge power can be greater than the capacity of the AC to DC converter in the vehicle, but also that the efficiency of the conversion is not dependent of the converter provided by the manufacturer at the time of making the vehicle. If DC charging can be made efficiently available to residences, then heavy and expensive level 2 charging equipment onboard vehicles could be omitted.
With level 2 power consumption, the probability that vehicle's charging will cause the residential electrical entry or main circuit panel to draw more than its allowed power budget (and thus cause the main breaker to trip with the result that the panel is disconnected from the distribution transformer) is quite low. However, when a load greater than 7 kW is added to most domestic electrical panels, and for a duration of a number of hours, the risk increases that the total power budget of the domestic electric panel will be exceeded.